1. Technical Field
The invention relates to hydrocarbon recovery from a subterranean hydrocarbon-bearing formation.
2. Background Information
Kill fluids are commonly placed in a wellbore during oil field operations, including drilling, wellbore completions, and workovers, to prevent the intrusion of formation fluids into the wellbore while the well is open. The kill fluid is often maintained in the wellbore for the entire duration of the operation.
Conventional kill fluids known in the art are typically aqueous liquids, which contain a weighting agent, such as inert inorganic solids in solution or suspension, to increase the density of the fluid. The weighted kill fluid applies a hydrostatic pressure against the formation fluid, which is greater than the pressure exerted by the formation fluid attempting to intrude into the wellbore. This overbalanced hydrostatic pressure prevents the intrusion of formation fluids into the wellbore during performance of the given oil field operation which is necessary from an operational standpoint to prevent interference from formation fluids and which is also necessary from a safety standpoint. Maintenance of a sufficient hydrostatic pressure in the wellbore reduces the potential of a well kick or blow out.
Thickeners ar often included in weighted kill fluids known in the art for leakoff inhibition. See, for example, Hudson et al., SPE Paper No. 10652, which discloses a weighted brine containing a fluid loss control agent, or U.S. Pat. No. 4,391,925, which discloses a multi-phase kill fluid comprising a number of constituents including a hydrocarbon, a surfactant, a clay and an organic polymer. Advantageous kill fluids are those which prevent formation fluid intrusion into the wellbore while preventing appreciable wellbore fluid leakoff into the formation. Fluid leakoff can undesirably result in formation damage, i.e., permeability reduction, which is manifested in reduced hydrocarbon recovery from the formation or reduced injectivity into the formation.
Despite the existence of numerous kill fluids in the art, many have limited utility. A need exists for a kill fluid having utility in hydrocarbon recovery operations over a broad range of operating conditions which can be encountered in situ. Specifically, a need exists for a kill fluid which effectively maintains a sufficient hydrostatic pressure in the wellbore under adverse conditions to prevent or minimize the intrusion of formation fluids into the wellbore without exhibiting significant leakoff into the formation or without significantly damaging the hydrocarbon formation.